The present invention pertains to an improved roller type feed device for sewing machines.
As is well known, such feed devices consist essentially of a pair of contiguous rollers with one thereof being rotatably driven. A work piece is advanced between the rollers by means of an intermittently driven unidirectional clutch having a braking unit operatively associated therewith.
As is well known, an intermittently driven unidirectional clutch is adapted to transform a pivotal movement generated by an eccentrically driven connecting rod mechanism into a unidirectional intermittent rotational movement. The braking unit serves to stop rotation of the drive feed roller after it has been caused to rotate a predetermined distance effected by the connecting rod mechanism to which it is operatively connected.
Additionally, the known types of intermittently driven clutches generally include a driving or actuating mechanism and a clamping unit with the latter serving to prevent rotation of the feed roller in a direction opposite that for effecting advance of a workpiece.
Usually, in such types of roller feed devices, the unidirectional clutch is located within one of the two rollers.
As is well known, sewing machines are required to operate at what is considered high speed and the frequency of oscillations transmitted to the feed wheel by the eccentrically driven connecting rod mechanism are of sufficient number so as to cause inadequate braking by the braking unit operatively associated therewith. As described above these braking units are intended to prevent over-travel of the drive feed roller during the performance of its intended function.
Additionally, the known forms of braking units are of the type in which the braking elements are engaged during the actual actuation of the feed roller causing a dissipation in heat of a portion of their effective braking force. Such braking units are not considered economical, reliable or efficient for they are subject to what is considered premature wear of the braking elements as well as frequent adjustments thereto in order to maintain effective braking.
With the feed roller capable of being incrementally advanced at selected rotational velocities, the limited size of the braking unit which the device can accommodate presents another disadvantage for it is obvious that the braking force should be increased with an increase in velocity of said feed roller.